1. Field of the Invention
This invention relates to light measuring apparatus and more particularly to optical interferometers used for electromagnetic frequency spectrum analysis.
2. Description of the Prior Art
Interferometers have been used for many years to measure and to analyze the frequency spectra of electromagnetic radiation. In particular, optical interferometers are commonly used to compute spectroscopic data such as line positions, intensities, and absorption coefficients. Interferometers are also used to monitor chemical processes, to identify the composition of gaseous samples at very low concentrations, and to plot the spectral signatures of remote emission plumes and thermal sources.
One type of interferometer in use today is the Michelson interferometer. The Michelson interferometer includes a half-silvered mirror or beam splitter placed at an angle of 45.degree. with respect to the electromagnetic radiation being measured. The beam splitter divides the radiation into two parts, and each part is directed along a separate perpendicular path within the interferometer. One part of the radiation is reflected off of a fixed mirror while the other part is reflected off of a movable mirror. The two parts are thereafter recombined at the beam splitter and optically interfere with each other to a degree proportional to their phase displacement. The phase displacement between the two parts is generated by the inequality in the path lengths between the movable mirror and fixed mirror.
Although the basic principles and general operation of Michelson interferometers are well known, most of these instruments have mechanical limitations and operational handicaps. For example, during operation most interferometers develop substantial vibrations that interfere with the spectral measurements. These vibrations are generated either by the motor and drive line for the movable mirror or from the bearings supporting the movable mirror. Further, the prior art interferometers cannot quickly damp out these vibrations once developed. Also, these prior art instruments cannot be subjected to either rugged environments, mechanical shock or wide temperature variations; and any occurrence thereof usually requires extensive readjustment of the instrument and repetition of the measurements.